Interaction of fibronectin (FN) cell binding fragments and interleukin-8 (IL-8) in regulating neutrophil chemotaxis

Fibroblasts-Warriors at the Intersection of Wound Healing and Disrepair

Wound healing is triggered by inflammation elicited after tissue injury. Mesenchymal cells, specifically fibroblasts, accumulate in the injured tissues, where they engage in tissue repair through the expression and assembly of extracellular matrices that provide a scaffold for cell adhesion, the re-epithelialization of tissues, the production of soluble bioactive mediators that promote cellular recruitment and differentiation, and the regulation of immune responses. If appropriately deployed, these processes promote adaptive repair, resulting in the preservation of the tissue structure and function. Conversely, the dysregulation of these processes leads to maladaptive repair or disrepair, which causes tissue destruction and a loss of organ function. Thus, fibroblasts not only serve as structural cells that maintain tissue integrity, but are key effector cells in the process of wound healing. The review will discuss the general concepts about the origins and heterogeneity of this cell population and highlight the specific fibroblast functions disrupted in human disease. Finally, the review will explore the role of fibroblasts in tissue disrepair, with special attention to the lung, the role of aging, and how alterations in the fibroblast phenotype underpin disorders characterized by pulmonary fibrosis.

Tumor Necrosis Factor-α and IL-17A Activation Induces Pericyte-Mediated Basement Membrane Remodeling in Human Neutrophilic Dermatoses

Sweet syndrome (SS) is a prototypical neutrophilic dermatosis, a class of inflammatory diseases marked by elevated levels of tumor necrosis factor (TNF)-α and IL-17A, pathologic neutrophil recruitment, and microvascular remodeling. Histologic analyses of four matrix proteins-collagen I and IV, laminin, and fibronectin-in skin biopsies of patients with SS reveal that the basement membrane of dermal postcapillary venules undergoes changes in structure and composition. Increased neutrophil recruitment in vivo was associated with increases in collagen IV, decreases in laminin, and varied changes in fibronectin. In vitro studies using TNF-α and IL-17A were conducted to dissect basement membrane remodeling. Prolonged dual activation of cultured human pericytes with TNF-α and IL-17A augmented collagen IV production, similar to in vivo remodeling. Co-activation of pericytes with TNF-α and IL-17A also elevated fibronectin levels with little direct effect on laminin. However, the expression of fibronectin- and laminin-specific matrix metalloproteinases (MMPs), particularly MMP-3, was significantly up-regulated. Interactions between pericytes and neutrophils in culture yielded even higher levels of active MMPs, facilitating fibronectin and laminin degradation, and likely contributing to the varied levels of detectable fibronectin and the decreases in laminin observed in vivo. These data indicate that pericyte-neutrophil interactions play a role in mediating microvascular changes in SS and suggest that targeting MMP-3 may be effective in protecting vascular wall integrity.

The possible role of granzyme B in the pathogenesis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a highly prevalent inflammatory lung condition characterized by airways disease and emphysema, and the precise mechanism of pathogenesis is poorly understood. The consistent features of COPD include protease-antiprotease imbalance, inflammation and accelerated aging caused by apoptosis or senescence. One family of molecules involved in all of these processes is the granzymes, serine proteases with the best-known member being granzyme B (GzmB). The majority of GzmB is released unidirectionally towards target cells, but GzmB can also be released nonspecifically and escape into the extracellular environment. GzmB is capable of cleaving extracellular matrix (ECM) proteins in vitro, and the accumulation of GzmB in the extracellular milieu during chronic inflammation in COPD could contribute to ECM degradation and remodelling and, consequently, the emphysematous phenotype in the lung. Preliminary studies suggest that increased GzmB expression is associated with increased COPD severity, and this may represent a promising new target for drug and biomarker discovery in COPD. In this paper, we review the potential pathogenic contributions of GzmB to the pathogenesis of COPD.

Cytokines derived from cultured skeletal muscle cells after mechanical strain promote neutrophil chemotaxis in vitro

We tested the hypothesis that cytokines derived from differentiated skeletal muscle cells in culture induce neutrophil chemotaxis after mechanical strain. Flexible-bottom plates with cultured human muscle cells attached were exposed to mechanical strain regimens (ST) of 0, 10, 30, 50, or 70 kPa of negative pressure. Conditioned media were tested for the ability to induce chemotaxis of human blood neutrophils in vitro and for a marker of muscle cell injury (lactate dehydrogenase). Conditioned media promoted neutrophil chemotaxis in a manner that was related both to the degree of strain and to the magnitude of muscle cell injury (ST 70 > ST 50 > ST 30). Protein profiling using a multiplex cytokine assay revealed that mechanical strain increased the presence of IL-8, granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor, monocyte chemotactic protein (MCP)-1, and IL-6 in conditioned media. We also detected 14 other cytokines in conditioned media from control cultures that did not respond to mechanical strain. Neutralization of IL-8 and GM-CSF completely inhibited the chemotactic response for ST 30 and ST 50 and reduced the chemotactic response for ST 70 by 40% and 47%, respectively. Neutralization of MCP-1 or IL-6 did not reduce chemotaxis after ST 70. This study enhances our understanding of the immunobiology of skeletal muscle by revealing that skeletal muscle cell-derived IL-8 and GM-CSF promote neutrophil chemotaxis after injurious mechanical strain.

Mechanical loading and injury induce human myotubes to release neutrophil chemoattractants

The purpose of this study was to 1) test the hypothesis that skeletal muscle cells (myotubes) after mechanical loading and/or injury are a source of soluble factors that promote neutrophil chemotaxis and superoxide anion (O(2)(-).) production and 2) determine whether mechanical loading and/or injury causes myotubes to release cytokines that are known to influence neutrophil responses [tumor necrosis factor-alpha (TNF-alpha), IL-8, and transforming growth factor-beta1 (TGF-beta1)]. Human myotubes were grown in culture and exposed to either a cyclic strain (0, 5, 10, 20, or 30% strain) or a scrape injury protocol. Protocols of 5, 10, and 20% strain did not cause injury, whereas 30% strain and scrape injury caused a modest and a high degree of injury, respectively. Conditioned media from strained myotubes promoted chemotaxis of human blood neutrophils and primed them for O(2)(-). production in a manner that was dependent on a threshold of strain and independent from injury. Neutrophil chemotaxis, but not priming, progressively increased with higher magnitudes of strain. Conditioned media only from scrape-injured myotubes increased O(2)(-). production from neutrophils. Concentrations of IL-8 and total TGF-beta1 in conditioned media were reduced by mechanical loading, whereas TNF-alpha and active TGF-beta1 concentrations were unaffected. In conclusion, skeletal muscle cells after mechanical loading and injury are an important source of soluble factors that differentially influence neutrophil chemotaxis and the stages of neutrophil-derived reactive oxygen species production. Neutrophil responses elicited by mechanical loading, however, did not parallel changes in the release of IL-8, TGF-beta1, or TNF-alpha from skeletal muscle cells.

RGD- and MLD-disintegrins, jarastatin and EC3, activate integrin-mediated signaling modulating the human neutrophils chemotaxis, apoptosis and IL-8 gene expression

The effects of jarastatin (JT), a monomeric RGD-disintegrin, were compared with those of the heterodimeric MLD-disintegrin, EC3, on human neutrophil activation and functions. Both disintegrins inhibited neutrophil chemotaxis induced by fMet-Leu-Phe and were also potent chemotactic agents. These effects were accompanied by an increase in actin polymerization, and both were inhibited by genistein, a tyrosine kinase inhibitor. While JT, but not other RGD-disintegrins, inhibited EC3-induced chemotaxis, EC3 was not able to inhibit JT effect. The chemotactic effect of JT was blocked by anti-alpha(M) antibody whereas anti-alpha(9)beta(1) inhibited EC3 effect. Both JT and EC3 induced focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K) activation. Accordingly, LY294002, a PI3K inhibitor, impaired their chemotactic effect on neutrophils. JT induced Erk-2 translocation to nucleus and a delay of the spontaneous apoptosis of neutrophils in vitro. In contrast, EC3 inhibited Erk-2 activation and had a proapoptotic effect. These effects were reverted by PD98059, an MEK 1/2 inhibitor and blocked by z-VAD-FMK, a caspase inhibitor. In addition, JT, but not EC3, increased the IL-8 mRNA levels in neutrophils. The data indicate that JT and EC3 directly activate an integrin-coupled signaling and modulate the MAPK pathway in different ways, leading the neutrophils to express different functional response.

Inhibition of IL-8-mediated MAPK activation in human neutrophils by beta1 integrin ligands

Chemokine and integrin receptors must work in concert when circulating leukocytes mobilize toward a site of tissue inflammation or infection. In a previous study, we reported that ligation of the alpha5beta1 integrin with a 120-kDa cell-binding fibronectin fragment (120-kDa FN) in suspensions of human polymorphonuclear leukocytes (PMNLs) inhibited chemotaxis toward the chemokine called interleukin-8 (IL-8). Binding of chemokines to their receptors on leukocytes leads to the activation of heterotrimeric G proteins that initiate multiple signaling cascades, including p38 and p42/p44 mitogen-activated protein kinase (MAPK) pathways. In the present study, we examine the potential interaction of beta1 integrin ligation on chemokine-mediated MAPK signaling in human PMNLs. We demonstrate that blockade of the p42/p44 MAPK signaling pathway by the inhibitor PD98059 suppresses IL-8-mediated PMNL chemotaxis. Furthermore, when PMNLs are pretreated with 120-kDa FN or an activating antibody to beta1 integrins (TS2/16), IL-8-mediated phosphorylation of p42/p44 MAPK is also inhibited. In contrast, pretreating PMNL with a specific ligand (laminin-1) for the alpha6beta1 integrin does not suppress IL-8-mediated phosphorylation of p42/p44 MAPK. These observations demonstrate a desensitization of IL-8-mediated p42/p44 MAPK signaling in response to ligation of the alpha5beta1 integrin in PMNL. Also, they suggest an interplay between integrin and chemokine signaling during PMNL migration through the extracellular matrix.

Fibronectin fragments and their role in inflammatory arthritis

OBJECTIVES

To identify potential immunopathogenic links between fibronectin (Fn) fragmentation and the inflammatory response in chronic joint disease.

METHODS

Scientific papers involving studies of Fn fragments and inflammatory processes important in the pathogenesis of arthritis, including chondrolysis, synoviocyte growth and adhesion, polymorphonuclear leukocyte (PMN) and monocyte function, proteolysis, and immune complex activation were reviewed. In addition, reports identifying Fn fragments in synovial fluid (SF) were assessed.

RESULTS

A series of Fn fragments have been identified in arthritic SF by several investigators. Fn and fragments ranging from 30 to 200 kd are present in elevated concentrations in inflammatory SF. SF Fn fragments display reduced affinity for fibrin and collagen. The 29- and 50-kd amino terminal fragments mediate release of proteoglycan from articular cartilage by RGD-independent mechanisms. Fn fragments can induce fibroblast gene expression of metalloproteinases or can act as proteinases themselves. A 90-kd plasmin generated fragment possesses homology with streptokinase. Fragments mediate PMN chemotaxis and enhance proliferation of CD4+ lymphocytes as well as binding to the C1q component of complement and influencing the behavior of immune complexes.

CONCLUSIONS

Fn fragments can be functionally and biochemically characterized in diseased SF. Modification of fragment formation and inhibition of fragment function may have potential therapeutic value in the interruption of chronic synovial inflammation.

Agonist-induced adherence of equine neutrophils to fibronectin- and serum-coated plastic is CD18 dependent

Adherence to vascular endothelium and extracellular matrix proteins is a pre-requisite for neutrophil accumulation at sites of inflammation. In this study, equine neutrophil adherence to fibronectin and autologous serum-coated plastic in response to PAF, hrIL-8, hrC5a and PMA has been measured. In addition, the mechanisms involved have been investigated using monoclonal antibodies (MoAbs) against the beta2 integrin CD18. PAF and hrC5a caused similar, concentration dependent, increases in adherence to fibronectin- and serum-coated plastic (maximum responses 19 +/- 4% and 19 +/- 3% for PAF and 15 +/- 4% and 16 +/- 2% for hrC5a on fibronectin- and serum-coated plastic, respectively). Adherence in response to PMA, although not reaching a maximum over the time course studied, was of a similar magnitude on the two surfaces (41 +/- 1% and 38 +/- 2% with 10(-7) M PMA on fibronectin- and serum-coated plastic, respectively). In contrast, the maximum adherence caused by hrIL-8 was significantly lower on fibronectin- than on serum-coated plastic (9 +/- 3% vs. 17 +/- 2%; 10(8) x M hrIL-8). Pre-incubation with MoAbs against CD18 (H20A and 6.5E) caused concentration related inhibition of stimulus-induced adherence to both fibronectin- and serum-coated plastic. Equine neutrophil adherence in response to PAF, hrIL-8, hrC5a and PMA therefore appears to be mediated by a CD18 dependent mechanism.

Effects of jarastatin, a novel snake venom disintegrin, on neutrophil migration and actin cytoskeleton dynamics

A new disintegrin, an RGD-containing peptide of 6 kDa called jarastatin, was purified from Bothrops jararaca venom. It is a potent inhibitor of platelet aggregation induced by ADP, collagen, and thrombin. The effect of jarastatin on neutrophil migration in vivo and in vitro and on the actin cytoskeleton dynamics of these cells was investigated. Incubation in vitro with jarastatin significantly inhibited, in a concentration-dependent manner, the chemotaxis of human neutrophils toward fMLP, IL-8, and jarastatin itself. Despite this inhibitory effect, jarastatin induced neutrophil chemotaxis. A significant increase of F-actin content was observed in jarastatin-treated neutrophils. Furthermore, as demonstrated by confocal microscopy after FITC-phalloidin labeling, these cells accumulated F-actin at the plasmalemma, a distribution similar to that observed in fMLP-stimulated cells. Pretreatment of mice with jarastatin inhibited neutrophil migration into peritoneal cavities induced by carrageenan injection. The results suggest that binding of jarastatin to neutrophil integrins promotes cellular activation and triggers a dynamic alteration of the actin filament system and that this is one of the first event in integrin-mediated signaling.

Interleukin-8 (IL-8), melanoma growth-stimulatory activity, and neutrophil-activating peptide selectively mediate priming of the neutrophil NADPH oxidase through the type A or type B IL-8 receptor

The capacity of neutrophils to generate superoxide (O-2) can be enhanced by prior exposure to "priming" agents such as interleukin-8 (IL-8), melanoma growth-stimulatory activity (MGSA), and neutrophil-activating peptide (ENA-78). The biological effects of these chemokines are mediated by at least two distinct receptors: type A (IL-8-RA) and type B (IL-8-RB). Using neutralizing monoclonal antibodies to IL-8-RA and IL-8-RB, we have investigated the contribution each receptor makes to the priming response. Preincubation with IL-8, MGSA, or ENA-78 enhanced the ability of neutrophils to generate O-2 following stimulation with the bacterial peptide formyl-Met-Leu-Phe. The priming effect of IL-8 was eliminated by an anti-IL-8 monoclonal antibody (mAb) that is known to bind IL-8 with high affinity and prevent receptor occupancy. Incubation of neutrophils with a neutralizing mAb specific for IL-8-RA blocked IL-8-induced priming but had no effect on priming by MGSA or ENA-78. In contrast, treatment with a neutralizing mAb specific for IL-8-RB failed to inhibit the priming effect of IL-8 but blocked both MGSA and ENA-78-induced priming. These observations indicate that the priming effect of IL-8 on the neutrophil respiratory burst is predominantly mediated via IL-8-RA, whereas priming by MGSA and ENA-78 is mediated by IL-8-RB.